time.AddDate（）不适用于仅解析时间，并将日期设置为今天吗？

Question

https://play.golang.org/p/O1FWb9O97ld

func main() {
    //const longForm = "Jan 2, 2006 at 3:04pm (MST)"
    t1, _ := time.Parse("03:04:05", "12:03:30")
    fmt.Printf("current date time %v
", t1)
    now := time.Now().UTC()
    t1.AddDate(now.Year(), int(now.Month()), now.Day())
    fmt.Printf("current date time %v", t1)
}

Output current date time 0000-01-01 12:03:30 +0000 UTC current date time 0000-01-01 12:03:30 +0000 UTC

Essentially I parse only time but want to add today's date to it. But nothing changed after calling time.AddDate()

Answer 1

AddDate doesn't change the value of the receiver (the receiver isn't a pointer). You need to assign the value to something, e.g.

t1 = t1.AddDate(now.Year(), int(now.Month())-1, now.Day()-1)

I'm also subtracting 1 from the month and the day since they started out at 1 and 1.

This is probably a better way to do what you want:

func main() {
    //const longForm = "Jan 2, 2006 at 3:04pm (MST)"
    t1, _ := time.Parse("03:04:05", "12:03:30")
    fmt.Printf("current date time %v
", t1)
    hour, min, sec := t1.Clock()
    now := time.Now().UTC()
    year, month, day := now.Date()
    t1 = time.Date(year, month, day, hour, min, sec, 0, time.UTC)
    fmt.Printf("current date time %v
", t1)
}